Due to environmental aspects and increasing fuel prices the on-board air conditioning system is preferably turned off during the time an aircraft is parked on the ground, while the high density of passengers, the interior lighting, the large number of windows and the heavily insulated fuselage all contribute to raising the temperature of the cabin to uncomfortable levels, even without taking into account the local weather conditions. To deal with this situation, preconditioned air is conventionally supplied to the aircraft directly into the aircraft ventilation system. This may be done by connecting the aircraft either to a remote air conditioning unit, to an air conditioning unit fixed to the telescopic corridor of the terminal, or to a portable air conditioning unit, which is towed close to the aircraft.
WO2004/000646 e.g. relates to such air conditioning unit, which is affixed under the telescopic passenger bridge/corridor.
GB 771,756 discloses a towable air conditioning unit operating on the air cycle principle that can be easily moved towards an aircraft on the ground.
WO 2004/024561 describes an environmentally friendly device for supplying preconditioned air to an aircraft on the ground operating on the air cycle principle which, similar to the air conditioning systems generally installed in all modern aircrafts, provides refrigeration without the use of CFC gases. A great advantage of this device is its design as a rolling, self-contained device that is supplied with compressed air produced at a remote location (e.g. in a compressor in the airport building) through a compressed air hose, avoiding the need for a motor-driven compressor within the movable device itself.
The actual delivery of the preconditioned air is then done through a flexible and usually insulated air hose that connects the ground air conditioning unit with the internal ventilation system of the aircraft, possibly via intermediate, rigid and insulated air ducts.
As it will be understood, the use of such ground air conditioning units will be particularly useful under hot and humid weather conditions. The use of such devices is critical in the Middle East and in certain Asian countries for the comfort of passengers during boarding. Unfortunately, it has been observed that in these countries, where large airports have been and are being constructed, the average operating temperatures are often too high for a rapid cooling (known as “pull down”) of the aircraft with conventional ground air conditioning units. Similarly, it is difficult with conventional ground air conditioning units to maintain a comfortable cabin temperature with the full passenger load and with the heat-generating modern in-flight entertainment systems in operation, and this is even more critical for large commercial aircraft, such as the Airbus A 380-800, where the ratio of passengers in relation to cabin volume is particularly high.